hello ,
in most case with asus cards, it's more sure to flash a bios with the latest version, then flash again with the same modded version of this bios ... downgrade is not a good plan and may cause bugs ...

it's a strange thing in your case, may be the mod is incorrect and network card not working correctly or disabled ...

did you reset to bios default ?
did you try to re-flash the original bios ?

better to give a link to original and modded bios for bios experts ....

well i am totally new here and i am having same motherboard P5KPL-AM/PS with bios 0411
so will the above given "bios0411 modded SLIC 2.1 DELL" work on my motherboard to or i have to upload my bios ???
and which windows does this modded bios work with vista & 7 or gust 7.

And what else do i have to backup like MAC address mentioned above.
How do i get those